Declining catches have prompted the first genetic study on Cape snoek to better understand and protect the species’ sustainability.
By Marise Schoonraad, journalist at African Farming and Landbouweekblad
No previous genetic studies exist for snoek, unlike for other regional marine species, says Dr Sihle Mthethwa from the Department of Genetics at Stellenbosch University. Essential data on the species is needed, as catches have been declining in recent years, threatening the income and food security of local fishing communities.
After years of stable catches, snoek now appears more vulnerable than previously thought. A drop in catches is placing pressure on local fishers and opening the door for imports from New Zealand.
“Cape snoek is an iconic Western Cape fish with deep cultural roots and significant economic value,” says Mthethwa. “It is an affordable, reliable source of protein for low-income West Coast households and provides income for both subsistence and commercial fisheries. Yet the essential data needed to ensure its sustainability is lacking.”
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Warning Signs in Snoek Genetics
An analysis indicated lower genetic diversity in certain snoek populations, signalling long-term risks for population health. This likely reflects a decline in the effective population size, which is a key driver of a species’ survival, says Mthethwa.
A declining snoek population will hit small-scale fishers particularly hard. The sector is vital for jobs and food security in low-income communities along the West Coast. Snoek represents not just income but also cultural heritage and an affordable source of protein.
Without action, such as targeted conservation measures guided by genetic findings, fishers may struggle to compete with unregulated imports, which could potentially force many operations to close.
Study Reveals Distinct Snoek Populations
Mthethwa’s study aimed to confirm whether barracouta snoek from New Zealand was genetically similar to Cape snoek, to understand gene flow between different coastal regions, to determine whether snoek stocks from other areas could be introduced, and to investigate the genetic diversity of Cape snoek along the West Coast.
He obtained samples from multiple locations across the Southern Hemisphere and analysed the DNA to understand the evolutionary history, long-term population patterns, recent gene flow and population structure of snoek. He also compared South African samples from different time periods.
Population subdivision was expected because of the large distances along the West Coast, which limit gene flow between groups, Mthethwa says, yet it was surprising to detect this clearly in the South African samples.
The DNA analyses revealed that Cape snoek in West Coast waters comprise at least two genetically distinct groups that do not interbreed freely despite sharing the same location at the same time, with a possible third stock shared with Namibia.
Mthethwa also found evidence that genetic diversity and population numbers have declined in recent generations. The loss of diversity could make the species less able to cope with environmental and fishing pressures.
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Genetic Research Could Guide Fisheries Management
Mthethwa says the aim of the research was to raise awareness about the species and to ensure its sustainability and resilience through genetically informed management.
The findings highlight the risks of stock collapse if the loss of diversity and unique stock structures is ignored, he says.
Beyond measuring biomass, the research could help protect small-scale fishers from import competition while preserving jobs, food security and cultural value.
The most important next step is to determine the precise boundaries of the three genetic groups of Cape snoek – the two groups along South Africa’s West Coast and the possible third group shared with Namibia. By identifying their exact locations, specific catch limits and protection measures could be implemented for each group.
This would help protect weaker groups, particularly those in which declining genetic diversity has been observed. At the same time, healthier groups could be managed sustainably.
After that, long-term monitoring will be needed that goes beyond simple biomass counts, Mthethwa says. By tracking effective population size over roughly three fish generations, early warning signs of declines could be detected, allowing action to be taken in time to secure the future of Cape snoek.
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